Scanning proximity microscopes (AFM, STM, MFM) operate by scanning the surface of a sample with a probe. Such a probe can be used e.g. for topography measurements or as a nano-SRP (nano-Spreading Resistance) Probe, used for the determination of the resistance and carrier profile of a semiconductor element or for nano-potentiometry measurements of the electrical potential distribution on a semiconductor element. Such a probe usually consists essentially of a mounting block, a cantilever or stylus and a tip. The choice of the materials of which the mounting block, the cantilever and the tip are composed, strongly depends on the type of measurement the probe is intended for. For topography measurement a dielectric or a semi-conductive tip can be used whereas for resistance determination and nano-potentiometry a highly conductive tip preferably with high hardness and low wear is required.
In order to achieve a high resolution the tip of such a probe must have a very small radius of curvature. A classical probe tip, as e.g. described in the U.S. Pat. No. 5,399,232 consists of a single portion. Changing the dimensions of such a probe tip, in particular increasing the height, can be necessary to meet the specifications of the measurement setup in particular e.g. the tip to sample distance. An increase of the tip height leads to a significant increase of the aspect ratio. The mechanical stability of such high aspect ratio tips is limited, which makes them less suitable for electrical measurements where these tips are exposed to high forces being applied in order to provide a good electrical contact. Therefore stable and reliable classical probe tips can only be fabricated for a limited range of dimensions. Furthermore there is an ongoing effort and interest in continuously improving the detection resolution and consequently the probe resolution, which will even further limit the availability of reliable probe tips.
In the prior art a probe tip configuration is suggested which partly overcomes this problem. The U.S. Pat. No. 5,455,419 describes a probe tip configuration where a tip is arranged on a pedestal. By dividing the probe tip into a pedestal and a tip, one can adapt the dimensions of the pedestal according to the specifications of the measurement set-up whereas the dimensions of the tip can be optimised independently. In U.S. Pat. No. 5,455,419 tip, pedestal and cantilever are composed of a single material. It is desirable to adjust the maximum penetration depth into the sample. Because of the special tip arrangement the penetration is limited to the tip while the pedestal can make contact with the sample surface without significant penetration. The maximum penetration depth can be altered by changing the dimensions, in particular the height of the tip. But because tip and pedestal are composed of a single material this easy adjustment of a maximum penetration depth into the sample is not applicable without drastically reducing the resolution. Furthermore the characteristics of both the pedestal and the tip can not be adapted to the physical quantity to be measured using different tip shapes and materials.
Also in the prior art a method of making such a probe tip configuration is suggested. U.S. Pat. No. 5,282,924 describes a method of fabricating said probe tip configuration where a tip is arranged on a pedestal. Said tip and said pedestal are composed of a single material which does not allow an easy adjustment of a maximum penetration depth into the sample. Furthermore the characteristics of both the pedestal and the tip can not be adapted to the physical quantity to be measured using different tip shapes and materials. A further drawback of this method is that there is no solution provided to realise a highly conductive probe tip. Tip, pedestal and cantilever beam are formed out of a single substrate material such as silicon. The cited document does not describe how to fabricate a probe with a highly conductive tip preferably with high hardness and low wear as desired for e.g. resistance determination. With cited method it is also not possible to fabricate a probe where probe tip and pedestal are isolated from each other e.g. for easy penetration depth adjustment or to reduce the capacitive coupling of the probe tip configuration to the sample by forming a pedestal which is composed of insulating materials.